Determine whether cancer is associated with low-dose occupational x-ray exposure by evaluation of the risk of radiation-induced cancer mortality in 160,000 registered x-ray technologists of the American Registry of Radiologic Technologists (ARRT), and estimation of radiation dose received by the x-ray technologists. Prepare a study protocol detailing follow-up procedures and strategies for locating inactive and active ARRT members, methods for estimating radiation exposure categories, procedures for mailing questionnaires to all located members, and approaches to confirm histologically cancers identified from the mail questionnaires, death certificates, or medical records. Prepare methodsfor final categorization of radiation exposure, assist in setting up a dosimetry committee, code all collected data, andprovide a computer tape copy of the "clean" data set to the Project Officer. Analyses of the data set will be conducted by both the Contractor and the Project Officer.